Harold Nicholson, 59, was sentenced to 23-and-a-half years in jail in 1997 for selling the Kremlin sensitive information believed to include the identities of several American spies working in Russia.
The former CIA chief of station in Romania earned himself the dubious distinction of becoming the first American spy to face two sets of criminal charges stemming from the same events.
Under a plea agreement which should see him serve an additional eight years, Nicholson admitted that from 2006 to December 2008 he passed further information to Russia and received payment for past disclosures.
"Harold Nicholson has admitted not only betraying his country -- again -- but also betraying his family by involving his son Nathaniel in his corrupt scheme to get more money for his past espionage activities," said US attorney Dwight Holton.
Nicholson relayed information to his son during encounters at his prison in the western US state of Oregon. Nathaniel Nicholson then travelled to locations including San Francisco, Mexico City, Lima, and Nicosia to meet with Russian agents.
"At these meetings, Nathaniel provided the Russian Federation information from the defendant and collected money for defendant's past espionage activities," a Justice Department statement said.
Judge Anna Brown yesterday scheduled Nicholson's sentencing for January 18, 2011. His son Nathaniel was convicted last year and is due to be sentenced in December.
A group of 10 spies, many of whom had been working for years undercover in the United States as sleeper agents, returned to Russia in July in a sensational spy swap that saw Moscow send four Russian convicts to the West.
The Kremlin agents were arrested in an FBI swoop that initially threatened to derail a rapid improvement in Russia-US relations.